Neat idea to get your veg in.
Open up your "Articles & Videos" tab and you'll see "Sparkrecipes.com", click it. Then you'll see a tab for "Recipe Calculator". When you go to it you add the bulk ingredients and then punch in the number of servings it makes (in your case, ice cubes). Save the recipe.
Then when you go to your Nutrition Tracker, click the last tab that says "recipes" and you'll find it in the drop box.